The present invention relates in general to sewing machines, and in particular to a new and useful method and apparatus for sewing together two pieces of cloth while maintaining correct alignment of a pattern on the two pieces of cloth.
A method for the pattern-correct sewing together of two cloth parts or pieces having the same pattern structure is not yet known. A sewing machine is known (German OS 24 12 896) which can sew together two cloth parts in equal lengths. Here the length difference of the two ends of the cloth parts is measured by sensors, and via an evaluating system the positioning system for the feed means is influenced accordingly. Through German Pat. No. 24 37 377 a similar device is known, in which the feed correction is checked by a second sensor arrangement during sewing and the evaluating system carries out a correction of the feed related deviation.
In the arrangements according to the state of the art, therefore, only the offset of the ends of the cloth parts can be compensated during the sewing operation, in that the value of this offset is supplied to the evaluating system, which then, after calculation of the necessary correction, controls the displacement of the positioning system for the feed of the cloth parts. A pattern-correct sewing together of cloth parts is therefore not possible with the known arrangements. Instead, pattern-correct sewing was heretofore possible only by continuous visual control of the seamstress and correction when necessary. This work, however, requires great concentration and care and is possible only at very low sewing speeds with interruptions of the sewing operation.